The present invention relates in general to an improved passive microwave detection technique for early detection of cancerous tumors. More particularly, the invention relates to a system adapted to provide localized heating of subsurface tissue with the use of an active microwave transmitter in combination with a passive radiometer for detecting a temperature differential occasioned by the differential heating between the tumor and adjacent tissue.
Studies have been conducted on the ability to measure temperature gradients particularly deep within the body tissue in connection with clinical medicine and research. For example, see the articles to A. H. Barrett, P. C. Myers and N. L. Sadowsky, "Detection of Breast Cancer by Microwave Radiometry." Radio Science 12, No. 6(S), 167, 1977; Ronald A. Porter and Harry H. Miller, "Microwave Radiometric Detection and Location of Breast Cancer." (Preprint.); J. Bigu del Blanco and C. Romero-Sierra, "MW Radiometry: A New Technique to Investigate the Interaction of MW Radiation with Living Systems." 27th ACEMB, Philadelphia, Pa., Oct. 6-10, 1974. These temperature gradients occur, it is theorized, because of vascular insufficiency associated with the thermal characteristics of tumors. It is well known that a carcinoma or malignant tumor is normally hotter than the surrounding tissue. It is also known that, from "black body" theory, any perfectly absorbing body emits radiation at all frequencies in accordance with Planck's radiation law. A recent article on the differential heating characteristics is one by B. C. Giovanella, "Correlation of Thermosensitivity of Cells to Their Malignant Potential." Conference on Thermal Characteristics of Tumors: Applications in Detection and Treatment; New York Academy of Sciences, Mar. 15, 1979.
The application of thermal therapy (i.e., localized heating) has been used to reduce tumor size or to even destroy the tumor. It has been found that tumor temperatures greater than 45.degree. C. can be maintained with the normal tissue adjacent to the tumor at the same time remaining at or near normal body temperature. It has been reported by several investigators that cell tumor tissue will necrose at temperatures above 42.degree. C. See the articles by David N. Leff, "Hyperthermia-Hottest News in Cancer Therapy." Medical World News, May 14, 1979; Jozef Mendecki, Esther Friedenthal and Charles Botstein, "Effects of Microwave-induced Local Hyperthermia on Mammary Adenocarcinoma in C3H Mice." Cancer Research 36, 2113-2114, June 1976; James Schaeffer, "Treatment of Metastatic Osteogenic Sarcoma in Mice with Whole Body Hyperthermia and/or Irradiation." International Symposium on Cancer Therapy by Hyperthermia and Radiation, Washington, D.C., 1975. Thermal therapy used in conjunction with other conventional techniques involving drugs or radiation has proven to be effective (i.e., anti-cancer drugs act more effectively at elevated temperatures and, similarly, permit lower level X-ray treatment). The combination of microwave detection with infra red detection is reported by Barrett and Myer, supra.
In accordance with the present invention, there is provided a sensitive microwave radiometer technique for sensing subsurface temperatures wherein the technique is not invasive. It has been common in the past to employ a conventional thermistor probe inserted in the area of the tumor, and studies have been made with regard to the effect on the heating patterns induced by microwave diathermy apparatus. See the Articles by Thomas C. Cetas, "Temperature Measurements in Microwave Diathermy Fields: Principles and Probes." International Symposium on Cancer Therapy by Hyperthermia and Radiation, Washington, D.C., 1975; Len Yencharis, "Temperature Probe Designed For Cancer Therapy." Electronic Engineering Times, 18, Jan. 9, 1978. The results of these studies indicate that the heating pattern is altered considerably by the presence of the sensor.
The microwave radiometer of the present invention is in effect a very sensitive radio receiver capable of measuring temperature differentials down to 0.1.degree. C. or less. The receiver, when provided with a highly directional antenna and technique of observation, provides a reading of power picked up by the antenna. As mentioned previously, any perfectly absorbing body emits radiation at all frequencies in accordance with Planck's radiation law. The distribution of radiation is a function of both the temperature and wavelength or frequency. As the temperature of the body increases, the density of the radiation at all frequencies also increases. From this viewpoint, infra red thermography or radiometry, appears to be effective, however, the depth of penetration (depth of effective emission) becomes a limiting factor. The highest value of radiation density occurs in the optical region. Nevertheless, an appreciable amount of radiation exists at the microwave segment of the spectrum. In accordance with the present invention the power accepted in a known bandwidth by an antenna having defined characteristics can be accurately computed as a function of the temperature of the emitter.
As mentioned previously, a carcinoma or malignant tumor normally radiates more heat than the surrounding tissue. See the article by R. N. Lawson and M. S. Chughtai, "Breast Cancer and Body Temperature." Canadian Medical Association, Vol. 88, Jan. 12, 1963. Early detection, namely detection prior to invasion or metastases, requires the detection of tumors less than five millimeters in diameter with an associated temperature deviation of less than 0.2.degree. C. It has been found in accordance with the techniques of this invention that such early detection is quite accurate, and that tumors of relatively small size can be detected which heretofore have not been capable of detection by such conventional techniques as X-ray mammography.
Accordingly, one of the objects of the present invention is to provide an improved technique for the diagnosis and treatment of cancer employing a non-invasive microwave detection system.
Another object of the present invention is to provide in a single unit the combination of both a microwave transmitter or source and a passive detector or microwave radiometer.
A further object of the present invention is to provide a microwave system employing a sensitive passive microwave radiometer particularly adapted for sensing subsurface temperatures in combination with a solid state microwave transmitter for providing localized heating of subsurface tissue. With such a combined system, there is essentially a highlighting of the tumor to enhance detection, thus taking advantage of the differential heating characteristics of the tumor with respect to the surrounding tissue.
Still another object of the present invention is to provide an improved microwave system for the early detection of cancer and which is adapted for use, not only for detection purposes but also for treatment purposes.
Still a further object of the present invention is to provide a microwave system for cancer diagnosis which is totally battery operated to thus eliminate possible problems associated with line transients and the like.
Another object of the present invention is to provide an improved microwave system for the detection of cancerous tumors and which is non-invasive, thus, not requiring the use of any temperature sensing probes. The present invention employs a sensitive passive microwave radiometer particularly designed to sense subsurface temperatures.
Still another object of the present invention is to provide an improved microwave system for the detection of cancerous tumors and which is capable of sensing at a temperature resolution down to at least 0.1.degree. C.
A further object of the present invention is to provide an improved microwave system for the detection of cancerous tumors and which is particularly adapted for the detection of relatively newly-formed tumors of extremely small size.
Another object of the present invention is to provide, in a microwave system, an improved, extremely sensitive passive radiometer capable of measurements of temperature deviations even less than 0.1.degree. C.